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osanseviero

  • one year ago

I need to write a program that that prints the longest substring of s in which the letters occur in alphabetical order. For example, if s = 'azcbobobegghakl', then your program should print beggh How should this start?

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  1. e.mccormick
    • one year ago
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    hmm... well, you could look at each character and see if it is <= the next. Count how many are, then make a sub string based on that. The issue is when to discard it if you find a larger string.

  2. e.mccormick
    • one year ago
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    azcbobobegghakl az alphabetical, but len 2. zc bad cb good, but not loneger cbo good, 3, drop the 2. ob bad bo good, but not loneger ob bad be good, but not loneger beg good, but not loneger begg good, loneger drop the 3 beggh good, loneger drop the 4 ha bad ak good but not longer akl good but not longer

  3. e.mccormick
    • one year ago
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    That is basically what it would do. Now for the how, use ifs and boolian comparisons.

  4. osanseviero
    • one year ago
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    so i keep creating substrings and comparing lengths, and depending on their lengths i will keep the largest one

  5. e.mccormick
    • one year ago
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    Well, you only need two bufer strings. The longes one as the answer and the now being worked on one. If the now worked becomes longer than the answer, replace the answer. >>> 'a'<'b' True >>> 'c'<'b' False >>>

  6. osanseviero
    • one year ago
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    How can I compare it with values from before?

  7. e.mccormick
    • one year ago
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    Testing each character as you go will let you decide if it is time to reset the buffer string or to add to it.

  8. osanseviero
    • one year ago
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    I need to rest.I will come back in some hours

  9. e.mccormick
    • one year ago
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    OK. This should give you something to start with. You can see what it would do and some info on how. Work with that and see how far you get.

  10. osanseviero
    • one year ago
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    In human talking, this would be done with this: 1. Take the first character 2. Save it. 3. Take the second character. 4. Compare them Option 1: a. If first character is bigger than the second one, FALSE statement, continue with first character as the substring. b. If first character is smaller, TRUE statement, new substring is first character + second one. 5. Repeat

  11. osanseviero
    • one year ago
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    But this would just work for a continued string...I dont know how it would be done for a new substring

  12. e.mccormick
    • one year ago
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    Well, if the first character is bigger, then you want to reset or erase the buffer string. If it is smaller, then you want to add it to the buffer string.

  13. e.mccormick
    • one year ago
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    And after every time through those, you want to see if the buffeer string is longer than the answer string. If so, replace the answer string with the buffer string.

  14. osanseviero
    • one year ago
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    Why does this give a number as an answer? s=raw_input("Enter a word: ") buffer="" for i in range(len(s)-1): if s[i]<=s[i+1]: buffer=str(i)+str(i+1) if s[i]>=s[i+1]: buffer=buffer print("Longest substring in alphabetical order is: " + str(buffer))

  15. e.mccormick
    • one year ago
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    |dw:1382852135152:dw|

  16. e.mccormick
    • one year ago
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    buffer=str(i)+str(i+1) buffer=str[i]+str[i+1] You need to use [ ] for string arrays. And you only want to work on one character at a time.

  17. osanseviero
    • one year ago
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    why are the results numbers?

  18. e.mccormick
    • one year ago
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    str(i) is not the same as str[i]

  19. e.mccormick
    • one year ago
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    ``` >>> s = "this is a test" >>> s[1] 'h' >>> i=1 >>> s[i] 'h' >>> s(i) Traceback (most recent call last): File "<interactive input>", line 1, in <module> TypeError: 'str' object is not callable ```

  20. osanseviero
    • one year ago
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    It never gives me an answer :/ s=raw_input("Enter a word: ") substring="" for i in range(len(s)-1): if s[i]<s[i+1]: substring=str(i) + str(i+1) if s[i]>=s[i+1]: substring="" print("Longest substring in alphabetical order is: " + str(substring))

  21. e.mccormick
    • one year ago
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    Like I said, you will need two buffers to hold strings. Also, you still have str(i). That is the numbers. You need s[i]. Also, this is how you turn multiple things into one but keep the first thing as part: ``` >>> a = 'abc' >>> b = 'def' >>> c = 'hij' >>> a 'abc' >>> a = a + b + c >>> a 'abcdefhij' >>> ```

  22. osanseviero
    • one year ago
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    I have two hours to finish this :/ Can you give me a push?

  23. osanseviero
    • one year ago
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    It throws me this :( string indices must be integers, not str

  24. osanseviero
    • one year ago
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    s=raw_input("Enter a word: ") substring="" output="" for i in range(len(s)-1): if s[i]<s[i+1]: substring=substring+s[i] if len(substring)>len(output): output=substring else: substring="" print output

  25. osanseviero
    • one year ago
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    Forget it, no more time. I still want to achieve this

  26. thisSucks
    • one year ago
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    @e.mccormick doen't leave any question unanswered

  27. e.mccormick
    • one year ago
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    Some possible flow of control issues.

  28. osanseviero
    • one year ago
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    Let me check this

  29. e.mccormick
    • one year ago
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    Forgot to put all the yes/no on that.

  30. e.mccormick
    • one year ago
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  31. e.mccormick
    • one year ago
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    I also realized that you need to test the last character in there somewhere, which is why that has another if in it.

  32. osanseviero
    • one year ago
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    which is the use of for i=0?

  33. e.mccormick
    • one year ago
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    It is a way of showing a for loop in a diagram.

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